This invention relates to a control process and a control arrangement for a continuously variable speed transmission.
As a rule, several characteristic control curves are provided in such control arrangements. These characteristic control curves permit various operating modes of the continuously variable speed transmission, from a power-oriented operation to a consumption-optimized operation. However, even with a consumption-optimized characteristic control curve, transient operation of the vehicle, and particularly acceleration, must also be possible. Therefore, even a consumption-optimized characteristic control curve cannot achieve the minimum possible consumption for the selected operating point because the low reserve of motive force at that point makes acceleration of the vehicle almost impossible.
It is therefore an object of the invention to provide a control process and apparatus for a continuously variable speed transmission by means of which the internal-combustion engine can also be operated in its consumption-optimal points.
This object is achieved according to the invention, by recognizing a driving situation, referred to herein as a "constant driving method", in which only a low motive force reserve is required. When such an situation exists, according to the invention, the transmission ratio is adjusted so that the internal-combustion engine is then operated at its point of the lowest specific fuel consumption for the existing operating point of the vehicle. Since the invention operates as a supplement to a conventional basic control unit, the inherent conflict between the need for optimal consumption, on the one hand, and an acceleration capacity appropriate with respect to the traffic, on the other hand, can be resolved in that consumption-optimal operation is set only in particularly suitable (stable) driving situations.
In further advantageous embodiments of the invention, the "constant driving method" is recognized by means of testing steps. That is, it is determined whether there is a reserve of motive force. (The vehicle must not be operated at the limit of its output capacity anyhow.) It is also tested whether the power control element, for example, a throttle valve, is actuated so that it can be determined whether the driver is capable of influencing the power of the internal-combustion engine. Finally, it is tested whether there is an essentially constant driving; that is, whether, at the moment, the rates of change of the driving speed and of the position of the power control element are low.
To adjust the transmission ratio, a consumption-optimal desired rotational drive speed is first determined, and then, after a predetermined transition function (for example, a PT1 or PT2 felter), the actual rotational drive speed is adjusted to the desired speed. This approach takes into account the fact that the driver of the vehicle is indirectly involved in the events because, in order to maintain the power, and therefore the driving speed of the vehicle, he must change the position of the power control element so that the power of the internal-combustion engine is maintained. The driver may also of course be replaced by an automatic speed control system, if it exists. In either case, the predetermined transition function is required in order to be able to carry out the change of the transmission ratio such that the driver or the speed control system, for the adaptation, can follow the position of the power control element as easily as possible. As a result, jerky transitions and annoyance to the driver are avoided. With an ideal design of the transition function, the change of the transmission ratio can take place in a manner such that the driver does not even notice it.
In the suggested test for steady-state driving, during an extended monitoring period, the integrals of the rates of change of the vehicle driving speed and the position of the power control element are monitored. This ensures that a change of the transmission ratio which, as mentioned above, reduces the consumption, but also the acceleration capacity of the vehicle, is initiated only when the driving situation in fact allows it. For this purpose, it is not the integral of the changes which is formed but rather the integral of the rate of the change, in order to detect all changes, whether they are positive or negative.
In summary the invention provides an arrangement for recognizing a driving situation such as may be found, for example, on limited access highways in moderate traffic, where there is little need for a higher output capacity of the internal-combustion engine caused by gradients, passing maneuvers or driving at or near the maximum speed. Advantageously, no separate adjusting devices are required; rather, an existing control arrangement for a continuously variable speed transmission can be supplemented by the invention without any further expenditures. The required readjustment of the position of the power control element takes place in a particularly simple manner by the driver himself or, in a slightly more comfortable manner, by means of an existing speed control system.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.